1. Field
The example embodiment is related in general to auxiliary equipment for industrial boilers such as regenerative air preheaters. More particularly the example embodiment is directed to a forced oscillation seal to prevent leaks of air to gas in these preheaters.
2. Related Art
A regenerative air preheater is heat recover equipment which transfers part of the heat from the combustion products (gases) produced during boiler operation to the air that is introduced to the boiler firebox through air ducts, so as to provide a hot air stream with a temperature that is higher than the environmental air. By using such recovering equipment, it is possible to achieve savings in the fuel consumption equal to the recovered heat, thus making it possible to recover the investment in the regenerative air preheater in a single year, in full capacity operation, or in 1.5 years when the preheater works under normal operating conditions.
Regenerative air preheaters are rotative heat exchangers with moving parts, one of which being its rotor. The rotor includes a plurality of heat transfer elements, called baskets. The rotor is also formed by segmented plates referred to as diaphragms, where the traditional or radial seals are arranged. These seals function to seal the polished surface of the ends of the plates/diaphragms, which are used to separate the gas side from the air side, and prevent the leaks or leakage of air to the hot combustion gas flowing in the opposite side. These air leaks cause an increase in power consumption of the forced draft fan (e.g., equipment that drives the air for the combustion through the regenerative air preheater), such that the industrial boiler cannot reach its full generation capacity, due to the lack of air when the air leaks are so high. Typically, regular or normal leaks range between 7% and 10%, and high leaks range between 11% and 35%.
U.S. Patent application No. 2009-0145574 discloses a seal for what is known as a Ljungstrom preheater of the prior art. The radial seals are made of a flexible material. However, such seals represent a high movement resistance between the rotor and a rotor drive unit, increasing the load and risk.